The control of iron precipitation in the presence of dissolve calcium is important in aqueous pigment dispersions, color strength improvement, ore flotation, manufacture of pulp and paper, slurry viscosity reduction, metal treating operations, textile processing, and water treatment.
While organophosphonates (e.g. amino tri(methylphosphonic acid) and hydroxyethylidene diphosphonic acid) and polyphosphates (e.g. sodium tripolyphosphate and sodium hexametaphosphate) have been used to inhibit the precipitation of iron, the organophosphonates are unfortunately sensitive to calcium hardness and prone to form calcium phosphonate precipitates. Polyphosphates are not thermally stable and will hydrolyze in an aqueous system to form orthophosphate which is extremely sensitive to calcium.
For these reasons, the use of the organophosphonates and polyphosphates heretofore in controlling iron precipitation have not been completely satisfactory. We have now discovered that copolymers of sodium styrene sulfonate and methacrylic acid are highly active iron dispersants. The copolymers of this invention are insensitive to calcium hardness and are thermally stable.